The present invention relates to a sheet feeder with a side pulling mark for subsequent sheet alignment, which is provided with a stop strip and with at least one pulling element actuated in the rhythm (cycle time) of the sheet feeder and moving back and forth transversely to the sheet run direction; this pulling element grasps the sheet to be aligned and pushes it against the stop strip.
With known arrangements of this type the sheet to be aligned is clamped mechanically from the top and bottom between two pressure surfaces and then moved to the side. As a rule, this is done by an up and down moving, freely rotating roller and a counter rail which can contact the roller and moves transversely to the run direction. There also have been known arrangements where two rollers act jointly to form the pressure surfaces grasping the sheet to be aligned. Since, however, the pressure forces required to ensure reliable sheet transport depend on the weight of the material to be handled, when processing thick or large-size and hence heavy material, there results great stress on the sheet to be aligned which may lead to permanent material deformations and visible clamping marks or traces. Particularly when processing cardboard or corrugated cardboard experience shows this to be very difficult, since even small pressure forces are sufficient to permanently deform the material.
Another important shortcoming of the known arrangements is that the sheet to be aligned must be equally accessible during the pulling process from both sides, i.e. from above and below. However, since the sheets arrive on the feeder table not individually, but in a so-called fish-scale like pattern, the sheet alignment can be started only when the overhanging end of the preceding sheet is pulled from the region of the side pull mark and is pulled into the following processing machine. Because of this waiting period there remains only a relatively short waiting period for the side alignment. Therefore, the control curves for controlling the pulling elements must have very steep start-up surfaces which with the present hourly runs impairs the stability and safety of operation. Also, because of these waiting periods it is not possible to feed sheet after sheet without gaps. With sheet feeders working with printing presses, the cylinder circumference which cannot be used in the area of the pit reduces this disadvantage; however, with "Raschier" machines such a gapless sheet sequence is not only desirable, but necessary to avoid dirtying or damaging of the sheet guide rollers, etc.
The known arrangements can be modified, of course, from the so-called pull motion to a push motion, to align heavy sheets by pushing from the side. But aside from the construction expense there is the danger that the slide (push) motion results in the sheet fore edge from the forward marks. Also, the push element may collide with the subsequent sheet.
Therefore, arrangements as known from German Pat. No. 617,605 have been used where disks are driven at sheet speed and located in associate recesses in the feeder table; these disks have an eccentric suction nozzle which pull the sheet above them by applying a vacuum and move it, depending on their distance from the axis of rotation, in parallelogram fashion forward and to the side and deposit it at the forward and side marks. To form the forward and side marks, the known arrangement has merely a simple stop strip. The known arrangement grasps the sheet to be aligned exclusively from the bottom so that accessibility from above is not necessary. Exact sheet alignment, particularly, laterally, is not possible with such arrangements since the edge position of the individual sheets differs widely, so that with the known arrangement which only permits sheet displacement by a fixed amount, this difference is present also in the area of the side marks. There is the danger that relatively far displaced sheets are not brought all the way to the stop and therefore cannot be aligned, and that less displaced sheets cause crumpling in the area of the stop strip. The resulting disadvantages regarding the possible work result are eminent. Also, the known arrangement leads to relative motions between the held sheets and the rotating disks. It must be feared that even this leads to crumpling, etc. Also, air guidance and control is relatively difficult with the known arrangements.
It is, therefore, the object of the present invention to provide an arrangement where with relatively simple and inexpensive means, a careful and still reliable treatment of the sheet is achieved, without regard to the material thicknesses to be processed; at the same time, a gapless sheet feeding is ensured, in addition to increased hourly output.
Another object of the present invention is to provide an arrangement of the foregoing character which may be economically maintained in service and which has a substantially long operating life.